"Marmot Precip works well in the rain and is quite packable, but the waterproofing will not hold up (abrades off) if you carry a heavy pack while wearing it. That being said I still use mine though it now leak across my shoulders and where the pack straps rode."

the same can be said for every rain jacket product out there - I never wear the jacket if I'm carrying the canoe, and more often than not, will not wear it with a heavy pack unless its raining hard - in a light rain, wearing the rain jacket and a pack will just make you get wet from sweat anyways - the less abuse, the longer any jacket will last.  The shoulder straps of a heavy pack stress the shoulder seams and the area under the straps, so even a very good gore tex jacket or whatever will eventually start to leak.
So I often will not use the jacket with the heavy load, but carry it, and then wear it for the return trip to get the second load.